Field of the Invention
The present invention relates to a radio access system and, more particularly, to a method for controlling transmit power in an environment, in which a user equipment (UE) is connected to two or more small cells, and an apparatus supporting the same.
Discussion of the Related Art
Wireless access systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless access system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.
Recently, the structure of a radio access system has changed to a structure in which small cells (e.g., pico cells, femto cells, etc.) having various shapes and small sizes are connected to a macro cell having a relatively large size. This aims to enable a user equipment (UE), which is an end user, to receive a high data rate to increase quality of experience in a state in which multilayered cells having vertical layers, in which conventional macro cells are fundamentally involved, are mixed.
However, in an environment in which a large number of small cells is arranged, a UE may be connected to two or more small cells to transmit and receive data. At this time, since the small cells are connected via a non-ideal backhaul, it is difficult to share data or scheduling information. At this time, the UE shall transmit control information of several small cells using a restricted uplink control channel. Accordingly, there is a need to transmit uplink control information using a method different from that of a legacy cellular system.